Dispersing feedstocks and processing materials

ABSTRACT

Biomass feedstocks (e.g., plant biomass, animal biomass, and municipal waste biomass) are processed to produce useful products, such as fuels. For example, systems are described that can convert feedstock materials to a sugar solution, which can then be fermented to produce ethanol. Biomass feedstock is dispersed in a liquid medium and then saccharified.

RELATED APPLICATIONS

This application is a divisional application of co-pending U.S.application Ser. No. 12/949,004, filed Nov. 18, 2010, which claimspriority to U.S. Provisional Application No. 61/296,658, filed Jan. 20,2010. The complete disclosure of these applications are incorporated byreference herein.

BACKGROUND

Cellulosic and lignocellulosic materials are produced, processed, andused in large quantities in a number of applications. Often suchmaterials are used once, and then discarded as waste, or are simplyconsidered to be waste materials, e.g., sewage, bagasse, sawdust, andstover.

Various cellulosic and lignocellulosic materials, their uses, andapplications have been described in U.S. Pat. Nos. 7,307,108, 7,074,918,6,448,307, 6,258,876, 6,207,729, 5,973,035 and 5,952,105; and in variouspatent applications, including “FIBROUS MATERIALS AND COMPOSITES,”PCT/US2006/010648, filed on Mar. 23, 2006, AND “FIBROUS MATERIALS ANDCOMPOSITES,” U.S. Patent Application Publication No. 2007/0045456.

SUMMARY

Processes are disclosed herein for saccharifying or liquifying amaterial, e.g., a cellulosic or lignocellulosic feedstock, by convertingthe cellulosic portion of the material to low molecular weight sugars,e.g., using an enzyme. The invention also relates to converting afeedstock to a product, e.g., by fermentation. The processes includeutilizing dispersing systems to disperse a fibrous and/or particulatefeedstock in a liquid medium.

The processes disclosed herein can utilize low bulk density materials,for example cellulosic or lignocellulosic feedstocks that have beenphysically pretreated to have a bulk density of less than about 0.75g/cm3, e.g., less than about 0.7, 0.65, 0.60, 0.50, 0.35, 0.25, 0.20,0.15, 0.10, 0.05. or less, e.g., less than 0.025 g/cm3.

Such materials can be especially difficult to disperse in liquids, e.g.,with water or a solvent system for saccharification, fermentation, orother processing. Due to their low bulk density, the materials tend tofloat on the surface of the liquid rather than being wetted out anddispersed into the liquid. In some cases, the materials can behydrophobic, highly crystalline, or otherwise difficult to wet. At thesame time, it is desirable to process the feedstock in a relatively highsolids level dispersion, in order to obtain a high final concentrationof sugar in the saccharified material, or a high concentration of thedesired product after processing (e.g., of ethanol or other alcohol(s)after fermentation). In some cases, utilizing the methods describedherein the solids level of the dispersion during processing can be, forexample, at least 10, 15, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or even atleast 50 percent by weight dissolved solids. For example, the solidslevel can be from about 10 to 50%, e.g., about 10-40%, 10-30%, or10-20%.

The inventors have found that the initial dispersion of a feedstockadded to a liquid can be enhanced by the use of certain equipment duringthe addition of the feedstock. The equipment described herein permitsthe feedstock or other solids or liquids, e.g., nutrients, to be quicklyand easily dispersed in the liquid, allowing a large quantity of thefeedstock to be added to the liquid efficiently. This efficientdispersion of feedstock contributes to reduced liquification time andthus high throughput, and facilitates the production of a high solidslevel mixture.

In one aspect, the invention features a method comprising saccharifyinga biomass feedstock in a vessel, the biomass feedstock having beendispersed in a liquid medium using a dispersing system comprising achamber and, within the chamber, a rotating member which draws thefeedstock and liquid medium into the chamber axially and expels adispersion of the feedstock in the medium from the chamber radially.

Some implementations include one or more of the following features. Thefeedstock can have a bulk density of, for example, less than about 0.5g/cm3. The liquid medium may include water. The method may furtherinclude delivering a saccharifying agent, e.g., an enzyme, to thevessel. The rotating member may function as an impeller and the actionof the rotating member within the chamber may be that of a centrifugalpump. The method may further include mixing with a jet mixer duringsaccharification. The rotating member may include mixing elementsarranged coaxially with a rotor that is disposed in rotor-statorrelationship with a side wall of the chamber. The dispersing system mayfurther include a jet mixer. The method may further include deliveringthe feedstock and/or a saccharifying agent to the vessel from a sourcedisposed outside the vessel, for example positioned above or next to thevessel, or at a distance from the vessel and in communication therewithby a conduit. Delivering the feedstock may include blowing the feedstockonto the surface of the liquid medium in the vessel. The method mayfurther include delivering a stream of liquid medium from the chamber ofthe dispersing system onto the feedstock on the surface of the liquidmedium to wet the feedstock. The feedstock may be in a substantially drycondition, e.g., 0.1 to 15% moisture content, prior to delivery to thevessel. The source from which the materials are delivered may include ahopper, which may be in communication with a vibrating device. Thedispersing system may include a plurality of dispersing devices.

In some embodiments, saccharifying includes adding the feedstock to theliquid medium in discrete increments, and dispersing each discreteincrement of feedstock into the liquid medium with the dispersing systembefore adding another increment of feedstock. The method may alsoinclude monitoring a glucose level of a mixture of the feedstock, theliquid medium and the saccharifying agent during saccharification.Additional feedstock and saccharifying agent may be added to the vesselduring saccharification and dispersed in the medium using the dispersingsystem.

In another aspect, the invention features a feedstock saccharificationapparatus that includes (a) a tank, (b) a delivery system configured todeliver a biomass feedstock and a liquid medium to the tank, (c) adispersing system configured to disperse the biomass feedstock in theliquid medium, (d) a saccharifying agent delivery device configured todeliver a metered amount of a saccharifying agent to the tank, and (e) amixer configured to mix the contents of the tank.

Some implementations include one or more of the following features. Thedispersing system comprises a chamber and, within the chamber, arotating member which draws the feedstock and liquid medium into thechamber axially and expels a dispersion of the feedstock in the mediumfrom the chamber radially. The apparatus further includes a controllerthat adjusts the operation of the feedstock delivery device and/or thesaccharifying agent delivery device based on input from the torquemonitor. In some cases, the mixer is a jet mixer. The delivery systemmay include a blower configured to blow the feedstock onto the surfaceof liquid in the tank, and the dispersing system may be configured todeliver a stream of liquid onto the feedstock on the surface of theliquid, wetting the feedstock.

In another aspect, the invention features a method that includessaccharifying a biomass feedstock in a vessel containing a liquidmedium, the biomass feedstock having been dispersed in the liquid mediumby blowing the biomass feedstock onto a surface of the liquid medium inthe vessel, contacting the feedstock on the surface with a stream ofliquid to wet the feedstock, and mixing the feedstock and liquid, e.g.,using a jet mixer.

In some implementations, the stream of liquid is delivered using apositive displacement pump.

In a further aspect, the invention features a method includingsaccharifying a biomass feedstock in a vessel, the biomass feedstockhaving been delivered to the vessel by blowing the biomass feedstockonto the surface of a liquid medium in the vessel, and dispersed in theliquid medium using a dispersing system comprising a chamber and, withinthe chamber, a rotating member which draws the feedstock and liquidmedium into the chamber axially and expels a dispersion of the feedstockin the medium from the chamber radially onto the feedstock on thesurface of the liquid medium.

The method may further include mixing the contents of the tank with ajet mixer.

In another aspect, the invention features a feedstock saccharificationapparatus that includes (a) a tank, (b) a delivery system configured todeliver a biomass feedstock and a liquid medium to the tank, comprisinga blower for blowing the biomass feedstock into the tank, (c) asaccharifying agent delivery device configured to deliver a meteredamount of a saccharifying agent to the tank, and (d) a mixer configuredto mix the contents of the tank.

The methods described herein generally provide relatively rapid andeffective wetting of a relatively high solids level of feedstock. Byincreasing the initial solids level of feedstock in the mixture, theprocess can proceed more rapidly, more efficiently and morecost-effectively, and a high resulting concentration can generally beachieved in the final product.

The saccharification processes described herein allow a cellulosic orlignocellulosic feedstock to be converted to a convenient andconcentrated form which can be easily transported and utilized inanother manufacturing facility, e.g., a facility configured to fermentsugar solutions to alcohols, to manufacture a product, e.g., a fuel suchas ethanol. Such concentrates can use less water, which can result insubstantial manufacturing and transportation cost savings.

Some processes disclosed herein include saccharification of thefeedstock, and transportation of the feedstock from a remote location,e.g., where the feedstock is produced or stored, to the manufacturingfacility. In some cases, saccharification can take place partially orentirely during transport.

In some cases, the systems described herein, or components thereof, maybe portable, so that the system can be transported (e.g., by rail,truck, or marine vessel) from one location to another. Such mobileprocessing is described in U.S. Ser. No. 12/374,549 and InternationalApplication No. WO 2008/011598, the full disclosures of which areincorporated herein by reference.

Exemplary products that can be produced by employing the methodsdescribed herein include hydrocarbons, proteins, alcohols (e.g., amonohydric alcohols or a dihydric alcohols), such as ethanol, n-propanolor n-butanol, carboxylic acids, such as acetic acid or butyric acid,salts of a carboxylic acid, a mixture of carboxylic acids and salts ofcarboxylic acids and esters of carboxylic acids (e.g., methyl, ethyl andn-propyl esters), ketones, aldehydes, alpha, beta unsaturated acids,such as acrylic acid, olefins, such as ethylene, and mixtures of any ofthese. Specific examples include ethanol, propanol, propylene glycol,butanol, 1,4-butanediol, 1,3-propanediol, methyl or ethyl esters of anyof these alcohols, methyl acrylate, methylmethacrylate, lactic acid,propionic acid, butyric acid, succinic acid, 3-hydroxypropionic acid, asalt of any of the acids and a mixture of any of the acids andrespective salts. These and other products are described in U.S.application Ser. No. 12/417,900, the disclosure of which is incorporatedby reference herein.

Bulk density is determined using ASTM D1895B. Briefly, the methodinvolves filling a measuring cylinder of known volume with a sample andobtaining a weight of the sample. The bulk density is calculated bydividing the weight of the sample in grams by the known volume of thecylinder in cubic centimeters.

All publications, patent applications, patents, and other referencesmentioned herein or attached hereto are incorporated by reference intheir entirety for all that they contain.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the enzymatic hydrolysis of celluloseto glucose.

FIG. 2 is a flow diagram illustrating conversion of a feedstock toethanol via production and transport of a glucose solution. FIG. 2A is adiagrammatic illustration of a saccharification system according to oneembodiment. FIG. 2B is a diagrammatic illustration of a saccharificationsystem according to another embodiment.

FIG. 3 is a schematic diagram of an ethanol manufacturing facility thathas been retrofitted to utilize the solutions and suspensions disclosedherein.

FIG. 4 is a diagrammatic perspective view of a dispersing systemaccording to one embodiment.

FIGS. 5 and 5A are diagrammatic cross-sectional and perspective views,respectively, of a dispersing device that can be used in the dispersingsystem shown in FIG. 4.

FIG. 6 is a diagrammatic perspective view of a dispersing systemaccording to another embodiment.

FIGS. 7 and 7A are diagrams illustrating alternative operating modes forthe dispersing system shown in FIG. 6.

FIG. 8 is a diagrammatic perspective view of a dispersing element thatcan be used in the dispersing system shown in FIG. 6.

FIGS. 9 and 9A are diagrams illustrating jet flow exiting a nozzle.

FIG. 10 is a diagrammatic perspective view of a jet-flow agitatoraccording to one embodiment. FIG. 10A is an enlarged perspective view ofthe impeller and jet tube of the jet-flow agitator of FIG. 10. FIG. 10Bis an enlarged perspective view of an alternate impeller.

FIG. 11 is a diagrammatic view of a blower for delivering a biomassfeedstock.

FIG. 12 is a cross-sectional view of a tank having a domed bottom andtwo jet mixers extending into the tank from above.

DETAILED DESCRIPTION

Using the methods described herein, biomass (e.g., plant biomass, animalbiomass, paper, and municipal waste biomass) can be processed to produceuseful intermediates and products such as organic acids, salts oforganic acids, anhydrides, esters of organic acids and fuels, e.g.,fuels for internal combustion engines or feedstocks for fuel cells suchas those described herein. Systems and processes are described hereinthat can use as feedstock materials cellulosic and/or lignocellulosicmaterials that are readily available, but often can be difficult toprocess materials, e.g., municipal waste streams and waste paperstreams, such as streams that include newspaper, kraft paper, corrugatedpaper or mixtures of these. Generally, if required, materials can bephysically treated for processing and/or after processing, often by sizereduction. Many of the processes described herein can effectively lowerthe recalcitrance level of the feedstock, making it easier to process,such as by bioprocessing (e.g., with any microorganism described herein,such as a homoacetogen or a heteroacetogen, and/or any enzyme describedherein), thermal processing (e.g., gasification or pyrolysis) orchemical methods (e.g., acid hydrolysis or oxidation). Biomass feedstockcan be treated or processed using one or more of any of the methodsdescribed herein, such as mechanical treatment, chemical treatment,radiation, sonication, oxidation, pyrolysis or steam explosion. Thevarious treatment systems and methods can be used in combinations oftwo, three, or even four or more of these technologies or othersdescribed herein and elsewhere.

The processes disclosed herein can utilize low bulk density materials,for example cellulosic or lignocellulosic feedstocks that have beenphysically pretreated to have a bulk density of less than about 0.75g/cm3, e.g., less than about 0.7, 0.65, 0.60, 0.50, 0.35, 0.25, 0.20,0.15, 0.10, 0.05. or less, e.g., less than 0.025 g/cm3. Bulk density isdetermined using ASTM D1895B. Briefly, the method involves filling ameasuring cylinder of known volume with a sample and obtaining a weightof the sample. The bulk density is calculated by dividing the weight ofthe sample in grams by the known volume of the cylinder in cubiccentimeters.

In order to convert the feedstock to a form that can be readilyprocessed, the glucan- or xylan-containing cellulose in the feedstock ishydrolyzed to low molecular weight carbohydrates, such as sugars, by asaccharifying agent, e.g., an enzyme or acid, a process referred to assaccharification. The low molecular weight carbohydrates can then beused, for example, in an existing manufacturing plant, such as a singlecell protein plant, an enzyme manufacturing plant, or a fuel plant,e.g., an ethanol manufacturing facility.

The materials that include cellulose can be treated with thesaccharifying agent by combining the material and the saccharifyingagent in a liquid medium, e.g., a solvent such as an aqueous solution.Methods for dispersing the material in the liquid medium quickly andefficiently are discussed in detail below. Once the material has beendispersed in the medium, the saccharifying agent, material and liquidmedium are mixed thoroughly, in some cases throughout saccharification.In some implementations, the material and/or the saccharifying agent areadded incrementally rather than all at once. For example, a portion ofthe material can be added to the liquid medium, dispersed therein, andmixed with the saccharifying agent until the material is at leastpartially saccharified, at which point a second portion of the materialis dispersed in the medium and added to the mixture. This process cancontinue until a desired sugar concentration is obtained.

Enzymes and biomass-destroying organisms that break down biomass, suchas the cellulose and/or the lignin portions of the biomass, contain ormanufacture various cellulolytic enzymes (cellulases), ligninases orvarious small molecule biomass-destroying metabolites. These enzymes maybe a complex of enzymes that act synergistically to degrade crystallinecellulose or the lignin portions of biomass. Examples of cellulolyticenzymes include: endoglucanases, cellobiohydrolases, and cellobiases(β-glucosidases). Referring to FIG. 1, a cellulosic substrate isinitially hydrolyzed by endoglucanases at random locations producingoligomeric intermediates. These intermediates are then substrates forexo-splitting glucanases such as cellobiohydrolase to produce cellobiosefrom the ends of the cellulose polymer. Cellobiose is a water-soluble1,4-linked dimer of glucose. Finally cellobiase cleaves cellobiose toyield glucose. Suitable cellulases will be discussed herein in a latersection.

The time required for complete saccharification will depend on theprocess conditions and the feedstock and enzyme used. Ifsaccharification is performed in a manufacturing plant under controlledconditions, the cellulose may be substantially entirely converted toglucose in about 12-96 hours. If saccharification is performed partiallyor completely in transit, saccharification may take longer.

In some cases, saccharification is performed at a pH of about 4 to 7,e.g., about 4.5 to 6, or about 5 to 6.

It is generally preferred that the final concentration of glucose in thesugar solution be relatively high, e.g., greater than 10%, or greaterthan 15, 20, 30, 40, 50, 60, 70, 80, 90 or even greater than 95% byweight. This reduces the volume to be shipped, and also inhibitsmicrobial growth in the solution. After saccharification, the volume ofwater can be reduced, e.g., by evaporation or distillation.

A relatively high concentration solution can be obtained by limiting theamount of medium, e.g., water, added to the feedstock with the enzyme.The concentration can be controlled, e.g., by controlling how muchsaccharification takes place. For example, concentration can beincreased by adding more feedstock to the solution. Solubility of thefeedstock in the medium can be increased, for example, by increasing thetemperature of the solution, and/or by adding a surfactant as will bediscussed below. For example, the solution can be maintained at atemperature of 40-50° C., 50-60° C., 60-80° C., or even higher.

Referring to FIG. 2, a process for manufacturing an alcohol, e.g.,ethanol, can include, for example, optionally physically pre-treatingthe feedstock, e.g., to reduce its size (step 110), before and/or afterthis treatment, optionally treating the feedstock to reduce itsrecalcitrance (step 112), and saccharifying the feedstock to form asugar solution (step 114). Saccharification can be performed by mixing adispersion of the feedstock in a liquid medium, e.g., water with anenzyme (step 111), as will be discussed in detail below. During or aftersaccharification, the mixture (if saccharification is to be partially orcompletely performed en route) or solution can be transported, e.g., bypipeline, railcar, truck or barge, to a manufacturing plant (step 116).At the plant, the solution can be bio-processed to produce a desiredproduct, e.g., ethanol (step 118), which is then processed further,e.g., by distillation (step 120). The individual steps of this processwill be described in detail below. If desired, the steps of measuringlignin content (step 122) and setting or adjusting process parameters(step 124) can be performed at various stages of the process, forexample just prior to the process step(s) used to change the structureof the feedstock, as shown. If these steps are included, the processparameters are adjusted to compensate for variability in the lignincontent of the feedstock, as described in U.S. Provisional ApplicationNo. 61/151,724, filed on Feb. 11, 2009, the complete disclosure of whichis incorporated herein by reference.

The mixing step 111 and saccharifying step 114 can be performed using,for example, either of the systems shown in FIGS. 2A and 2B. Thesesystems include a tank 136, which initially contains a liquid medium andlater contains a mixture 138 of liquid medium, feedstock andsaccharifying agent. The liquid medium is delivered to the tank througha valved piping system (not shown). The systems also include a hopper130, in communication with a dispersing unit 134. In the embodimentshown in FIG. 2B, the hopper 130 receives feedstock that has beentreated to reduce its size and optionally to reduce its recalcitrance(steps 110 and 112 above) by a feedstock pretreatment module 132. Inboth embodiments, the hopper may receive other dry ingredients, such asyeast and nutrients, e.g., from a supply 30. Optionally, a vibratingdevice 36 may be associated with the hopper, to facilitate delivery ofmaterial from the hopper. The system also includes a dispersing unit134. The liquid medium is drawn into the dispersing unit 134 from thetank, and returned to the tank by the dispersing unit via an outlet pipe137. The opening of outlet pipe 137 may be above the liquid level, asshown, or may in some instances be submerged in the liquid in the tank.In some cases, depending on the type of dispersing unit used (as will bediscussed below), the system may include a pump 139, e.g., a positivedisplacement pump, configured to circulate the liquid medium through thedispersing system, and/or a viscometer 141 to monitor the viscosity ofthe dispersion and activate the pump when the measured viscosity reachesa predetermined value.

In the embodiment shown in FIG. 2A, the feedstock is delivered to thesurface of the liquid medium in the tank, e.g., via a delivery device 32having a delivery conduit 34 (e.g., hose or pipe). The delivery device32 may also be associated with a vibrating device 36, to facilitate flowof material into the device. The delivery device 32 may be, for example,a blower configured to blow fibrous and/or particulate material from asource to a location remote from the source through a hose, e.g., aninsulation blower such as the FORCE 3 blower available from Intec,Frederick, Colo. An example of a blower 500 is shown schematically inFIG. 11. A hopper 502 of the blower 500 receives material from amaterial source 504, e.g., by drawing the material in through inlet 505via a vacuum 506. Once in the hopper, the material is deagglomeratedusing a rotating device 508, which includes rotating arms 510terminating in flexible paddles 512. The rotating device 508 also sweepsmaterial down through an opening 514 to an airlock 516. Delivery ofmaterial to the airlock is metered by a plate or valve 518. The airlock516 includes a plurality of rotating vanes 520 that define chambers 522.The lower portion of airlock 516 includes a passageway 524 through whichair blows from a compressed air supply (not shown) into an outlet tube(e.g., delivery conduit 34, FIG. 2A). The vanes sweep the material tothe passageway in individual portions, which are blown into the outlettube as soon as they are in place adjacent the passageway. The rotatingvanes 520 rotate sufficiently slowly that each chamber is in positionadjacent the passageway long enough so that both the portion of materialand a certain amount of air are delivered into the outlet tube. Thus,alternating portions of air and material are delivered to the outlettube. As the material passes down the outlet tube, which can be quitelong, the material and air mix, aerating the material and keeping itmoving smoothly through the outlet tube to the tank. The rate ofrotation of the rotating members in the agitator and the airlock isgeared together and can be varied by the user based on the feedstock,the length of the outlet tube, and other variables.

Alternatively, the material can be delivered to the surface of theliquid using other techniques, such as gravity feed or a screw conveyor.

In some implementations, the tank is provided with a flexible, airpermeable cover, or other device configured to allow air to vent fromthe tank during delivery of the feedstock, while preventing feedstockfrom blowing out of the tank and/or contaminants from entering the tank.

As the feedstock material is delivered through delivery conduit 34 ontothe surface of the liquid in the tank, liquid is discharged throughoutlet pipe 137 of the dispersing unit 134 onto the material. Thedischarged liquid wets the feedstock material, causing it to sink intothe liquid, where it can be dispersed by the dispersing unit 134,optionally in combination with the mixing action of a jet mixer 144,discussed below.

It is generally preferred that the dispersing unit 134 and the jet mixer144 are operating when the feedstock is delivered through the deliveryconduit.

In the embodiment shown in FIG. 2B, the feedstock is delivered to thetank via hopper 130, which may receive the feedstock from, for example,a feedstock treatment module 132, and enters the dispersing unit 134where it is dispersed in the liquid medium, e.g., water.

In both embodiments, a saccharifying agent is delivered to the tank froma hopper 140, which includes a metering device 142. The contents of thetank are mixed, e.g., by one or more jet mixers. A jet mixer 144 isrepresented diagrammatically in FIGS. 2A and 2B; examples of suitablejet mixers will be described in detail below, and are also described inU.S. Provisional Application No. 61/218,832, filed Jun. 19, 2009, thefull disclosure of which is hereby incorporated by reference herein. Thejet mixer produces a jet using a motor 146 that drives a pump and/or arotor (not shown). The torque exerted by the motor 146 correlates withthe solids level of the mixture in the tank, which in turn reflects thedegree to which the mixture has saccharified. The torque is measured bya torque monitor 148, which sends a signal to a motor 150 that drivesthe conveyor 130 and also to the metering device 142 of the hopper 140.Thus, the supply of the treated feedstock and the enzyme can beinterrupted and resumed as a function of the saccharification of thecontents of the tank. The data measured by the torque monitor can alsobe used to adjust the jet mixer, e.g., to a lower RPM for a mixer thatutilizes a rotor, or to a lower jet velocity for a pump-driven mixer.Instead of, or in addition to, the torque monitor, the system mayinclude an Amp monitor (not shown) that measures the full load amperageof the motor. In some cases, the jet mixer may include a variablefrequency drive (VFD) to allow the speed of the motor to be adjusted.

The system may also include a heat monitor (not shown) that monitors thetemperature of the liquid medium and adjusts the feed rate of thefeedstock and/or the mixing conditions in response to increases intemperature. Such a temperature feedback loop can be used to prevent theliquid medium from reaching a temperature that will denature the enzyme.

When one or more pumps are used in the systems described herein, it isgenerally preferred that positive displacement (PD) pumps be used, e.g.,progressive cavity or screw-type PD pumps.

In some cases, the manufacturing plant can be, for example, an existinggrain-based or sugar-based ethanol plant or one that has beenretrofitted by removing or decommissioning the equipment upstream fromthe bio-processing system (which in a typical ethanol plant generallyincludes grain receiving equipment, a hammermill, a slurry mixer,cooking equipment and liquefaction equipment). Thus, the feedstockreceived by the plant is input directly into the fermentation equipment.A retrofitted plant is shown schematically in FIG. 3. The use of anexisting grain-based or sugar-based ethanol plant in this manner isdescribed in U.S. Ser. No. 12/704,521, filed Feb. 11, 2010, the fulldisclosure of which is incorporated herein by reference.

In some embodiments, rather than transporting the saccharified feedstock(sugar solution) to a separate manufacturing plant, or even a separatetank, the sugar solution is inoculated and fermented in the same tank orother vessel used for saccharification. Fermentation can be completed inthe same vessel, or can be started in this manner and then completedduring transport as discussed above. Saccharifying and fermenting in asingle tank are described in U.S. Provisional Application No.61/296,673, filed Jan. 20, 2010, the full disclosure of which isincorporated herein by reference.

Generally, the oxygen level in the fermentation vessel should becontrolled, e.g., by monitoring the oxygen level and venting the tank oraerating the mixture as necessary. It is also desirable to monitor thelevel of ethanol in the vessel, so that when the ethanol level begins todrop the fermentation process can be stopped, e.g., by heating or theaddition of sodium bisulfite. Other methods of stopping fermentationinclude adding a peroxide (e.g., peroxy acetic acid or hydrogenperoxide), adding succinic acid or a salt thereof, cooling the contentsof the vessel, or reducing the oxygen sparge rate. Combinations of anytwo or more of these methods may be used. If fermentation is to beconducted or completed during transport, the transportation vessel(e.g., the tank of a rail car or tanker truck) can be fitted with acontrol unit that includes an oxygen monitor and ethanol monitor, and adelivery system for delivering sodium bisulfite (or other fermentationterminating additive) to the tank and/or a system for adjusting theparameters in the tank to stop fermentation.

If desired, jet mixing can be utilized during fermentation, and iffermentation is conducted in the same vessel as saccharification thesame equipment can be utilized. However, in some embodiments jet mixingis not necessary. For example, if fermentation is conducted duringtransport the movement of the rail car or tanker truck may provideadequate agitation.

Dispersing and Mixing

Dispersing

Dispersing unit 134 may include any type of dispersing equipment thatwets the feedstock with the liquid medium. Many dispersing units includea chamber and a rotor in the chamber positioned such that the feedstockand liquid medium are drawn towards the rotor axially, and forcedoutward radially to the periphery of the rotor and thus through theoutlet of the unit, in the manner of a centrifugal pump. Depending uponthe construction of the dispersing unit, a back-up pump may be required(pump 139, discussed above) to draw the fluid through the dispersingunit at high viscosities. Some dispersing units are constructed togenerate very high static fluid pressure within the unit; when suchunits are used a back-up pump is generally not required.

One example of a suitable dispersing system 300 is shown in FIGS. 4-5A.This system generates relatively low suction, and thus a back-up pump istypically used. Dispersing system 300 includes a receiving bin 302 whichcan receive feedstock from a larger hopper or bag (not shown) or othersource and deliver it to dispersing unit 301. Dispersing unit 301includes a housing 304, which defines a dispersing chamber 306 (FIG.5A), a liquid inlet 308, a solids inlet 310 (FIG. 5A) in communicationwith the bin 302, and an outlet 312. The dispersing system 300 alsoincludes a motor 314 that drives the dispersing unit 301, a user controlinterface 316, and a pressurized unit 318 that helps to maintain theintegrity of seals within the dispersing unit 301. A valve (not shown)is disposed between the receiving bin 302 and the solids inlet 310 tometer delivery of the solids to the dispersing unit 301.

The internal structure of the dispensing unit 301 is shown in FIGS.5-5A. After passing through solids inlet 310, the solids are moveddownward by an auger 320 as the solids are contacted by the liquidentering through liquid inlet 308. The liquid and solids are then mixedby a series of mixing paddles 322, and finally by a rotor 324 (shown indetail in FIG. 5A) which is disposed in a rotor/stator arrangementrelative to the side wall of the chamber 306. This series of mixingelements wets the solids with the liquid, at increasing levels of shear,resulting in a substantially homogeneous dispersion exiting through theoutlet 312. The impeller, by the Venturi principle, creates a largepressure differential between the chamber 306 and the bin 302, whichdraws a vacuum and thus helps to draw the material from the bin into thechamber.

Another suitable dispersing system 400 is shown in FIGS. 6-8. Thissystem is commercially available from IKA® Works, Wilmington, N.C.,under the tradename CMS 2000. Dispersing system 400, as supplied,includes a liquids tank 402. However, if desired the relatively smalltank 402 can be omitted and the remainder of the system piped into alarger tank, e.g., an industrial volume tank (not shown). System 400also includes a solids receiving funnel 403, a dispensing unit 401including a housing 404 having a structure similar to that of housing304 discussed above, a motor 414, a user control interface 416, and apressurized unit 418.

The primary difference between the dispersing system 400 and thedispensing system 300 lies in the internal structure of the dispensingunits 401 and 301. The dispensing unit 401, shown in detail in FIG. 8,includes a rotor 420 which functions as an impeller and generates veryhigh static fluid pressure within the unit. As a result, the dispersingunit functions in the manner of a centrifugal pump, and a back-up pumpis generally not necessary, even at relatively high viscosities.

The rotor 420 draws the liquid from the tank into chamber 406 throughinlet 408 at high suction. The liquid and the solids (entering throughinlet 410) are drawn axially into the rotor 420 at high pressure, andexit the rotor 420 radially with high velocity turbulent flow thatdisperses the feedstock into the liquid. A substantially homogeneousdispersion exits the chamber via outlet 412 and is delivered to the tankfor saccharification.

The dispersing system 400 may be operated in various modes, examples ofwhich are shown in FIGS. 7 and 7A. In FIG. 7, the dispersing unit 401 isfed by loading the feedstock into a hopper 422 that is mounted on thesolids inlet of housing 404. A valve 424 controls delivery of thefeedstock to the dispersing unit 401. The feedstock can be loaded usingany desired delivery technique, e.g., manually, by conveyor, pneumaticloader, or the like. In FIG. 7A, the feedstock is suctioned out of a bagor bin 424 using a suction wand 426. In this case delivery of thefeedstock can be controlled by controlling the rate of suctioning. Otherarrangements may be used.

The feedstock may be delivered to the dispersing unit continuously orintermittently, and the dispersing system may be run in a recirculatingor “once through” mode. If desired, the dispersing unit can be used formixing during saccharification, after initial dispersion has beencompleted.

Jet Mixing

Once the feedstock has been substantially dispersed in the liquid, itmay be desirable to turn off the dispersing system and use a mixer thatrequires less energy for further mixing. Particularly advantageousmixers for this purpose are known as “jet mixers.” In general, suitablemixers have in common that they produce high velocity circulating flow,for example flow in a toroidal or elliptical pattern. Generally,preferred mixers exhibit a high bulk flow rate. Preferred mixers providethis mixing action with relatively low energy consumption. It is alsogenerally preferred that the mixer produce relatively low shear andavoid heating of the liquid medium, as shear and/or heat candeleteriously affect the saccharifying agent (or microorganism, e.g., inthe case of fermentation). As will be discussed in detail below, somepreferred mixers draw the mixture through an inlet into a mixingelement, which may include a rotor or impeller, and then expel themixture from the mixing element through an outlet nozzle. Thiscirculating action, and the high velocity of the jet exiting the nozzle,assist in dispersing material that is floating on the surface of theliquid or material that has settled to the bottom of the tank, dependingon the orientation of the mixing element. Mixing elements can bepositioned in different orientations to disperse both floating andsettling material, and the orientation of the mixing elements can insome cases be adjustable.

In some preferred mixing systems the velocity of the jet as it meets theambient fluid is from about 2 to 300 m/s, e.g., about 5 to 150 m/s orabout 10 to 100 m/s. The power consumption of the mixing system may beabout 20 to 1000 KW, e.g., 30 to 570 KW, 50 to 500 KW, or 150 to 250 KWfor a 100,000 L tank.

Jet mixing involves the discharge of a submerged jet, or a number ofsubmerged jets, of high velocity liquid into a fluid medium, in thiscase the mixture of biomass feedstock, liquid medium and saccharifyingagent. The jet of liquid penetrates the fluid medium, with its energybeing dissipated by turbulence and some initial heat. This turbulence isassociated with velocity gradients (fluid shear). The surrounding fluidis accelerated and entrained into the jet flow, with this secondaryentrained flow increasing as the distance from the jet nozzle increases.The momentum of the secondary flow remains generally constant as the jetexpands, as long as the flow does not hit a wall, floor or otherobstacle. The longer the flow continues before it hits any obstacle, themore liquid is entrained into the secondary flow, increasing the bulkflow in the tank or vessel. When it encounters an obstacle, thesecondary flow will lose momentum, more or less depending on thegeometry of the tank, e.g., the angle at which the flow impinges on theobstacle. It is generally desirable to orient the jets and/or design thetank so that hydraulic losses to the tank walls are minimized. Forexample, it may be desirable for the tank to have an arcuate bottom(e.g., a domed headplate), and for the jet mixers to be orientedrelatively close to the sidewalls, as shown in FIG. 12. The tank bottom(lower head plate) may have any desired domed configuration, or may havean elliptical or conical geometry.

Jet mixing differs from most types of liquid/liquid and liquid/solidmixing in that the driving force is hydraulic rather than mechanical.Instead of shearing fluid and propelling it around the mixing vessel, asa mechanical agitator does, a jet mixer forces fluid through one or morenozzles within the tank, creating high-velocity jets that entrain otherfluid. The result is shear (fluid against fluid) and circulation, whichmix the tank contents efficiently.

Referring to FIG. 9, the high velocity gradient between the core flowfrom a submerged jet and the surrounding fluid causes eddies. FIG. 9Aillustrates the general characteristics of a submerged jet. As thesubmerged jet expands into the surrounding ambient environment thevelocity profile flattens as the distance (x) from the nozzle increases.Also, the velocity gradient dv/dr changes with r (the distance from thecenterline of the jet) at a given distance x, such that eddies arecreated which define the mixing zone (the conical expansion from thenozzle).

In an experimental study of a submerged jet in air (the results of whichare applicable to any fluid, including water), Albertson et al.(“Diffusion of Submerged Jets,” Paper 2409, Amer. Soc. of CivilEngineers Transactions, Vol. 115:639-697, 1950, at p. 657) developeddimensionless relationships for v(x)r=0/vo (centerline velocity),v(r)x/v(x)r=0 (velocity profile at a given x), Qx/Qo (flow entrainment),and Ex/Eo (energy change with x):

(1) Centerline velocity, v(x)_(r=0)/v_(o):

${\frac{v( {r = 0} )}{v_{o}}\frac{x}{D_{o}}} = 6.2$

(2) velocity profile at any x, v(r)_(x)/v(x)_(r=0):

(3) Flow

${\log \lbrack {\frac{{v(r)}_{x}}{v_{o}}\frac{x}{D}} \rbrack} = {0.79 - {33\frac{r^{2}}{x^{2}}}}$

and energy at any x:

$\begin{matrix}{\frac{Q_{x}}{Q_{o}} = {0.32\frac{x}{D_{o}}}} & (10.21) \\{\frac{E_{x}}{E_{o}} = {4.1\frac{D_{o}}{x}}} & (10.22)\end{matrix}$

where:v(r=0)=centerline velocity of submerged jet (m/s),v_(o)=velocity of jet as it emerges from the nozzle (m/s),x=distance from nozzle (m),r=distance from centerline of jet (m),D_(o)=diameter of nozzle (m),Q_(x)=flow of fluid across any given plane at distance x from the nozzle(me/s),Q_(o)=flow of fluid emerging from the nozzle (m3/s),E=energy flux of fluid across any given plane at distance x from thenozzle (m³/s),E_(o)=energy flux of fluid emerging from the nozzle (m³/s).

(“Water Treatment Unit Processes: Physical and Chemical,” David W.Hendricks, CRC Press 2006, p. 411.)

Jet mixing is particularly cost-effective in large-volume (over 1,000gal) and low-viscosity (under 1,000 cPs) applications. It is alsogenerally advantageous that in most cases the pump or motor of the jetmixer not be submerged, e.g., when a pump is used it is generallylocated outside the vessel.

One advantage of jet mixing is that the temperature of the ambient fluid(other than directly adjacent the exit of the nozzle, where there may besome localized heating) is increased only slightly if at all. Forexample, the temperature may be increased by less than 5° C., less than1° C., or not to any measureable extent.

Jet-Flow Agitators

One type of jet-flow agitator is shown in FIGS. 10-10A. This type ofmixer is available commercially, e.g., from IKA under the tradenameROTOTRON™. Referring to FIG. 10, the mixer 200 includes a motor 202,which rotates a drive shaft 204. A mixing element 206 is mounted at theend of the drive shaft 204. As shown in FIG. 10A, the mixing element 206includes a shroud 208 and, within the shroud, an impeller 210. Asindicated by the arrows, when the impeller is rotated in its “forward”direction, the impeller 210 draws liquid in through the open upper end212 of the shroud and forces the liquid out through the open lower end214. Liquid exiting end 214 is in the form of a high velocity stream orjet. If the direction of rotation of the impeller 210 is reversed,liquid can be drawn in through the lower end 214 and ejected through theupper end 212. This can be used, for example, to suck in solids that arefloating near or on the surface of the liquid in a tank or vessel. (Itis noted that “upper” and “lower” refer to the orientation of the mixerin FIG. 10; the mixer may be oriented in a tank so that the upper end isbelow the lower end.)

The shroud 208 includes flared areas 216 and 218 adjacent its ends.These flared areas are believed to contribute to the generally toroidalflow that is observed with this type of mixer. The geometry of theshroud and impeller also concentrate the flow into a high velocitystream using relatively low power consumption.

Preferably, the clearance between the shroud 208 and the impeller 210 issufficient so as to avoid excessive milling of the material as it passesthrough the shroud. For example, the clearance may be at least 10 timesthe average particle size of the solids in the mixture, preferably atleast 100 times.

In some implementations, the shaft 204 is configured to allow gasdelivery through the shaft. For example, the shaft 204 may include abore (not shown) through which gas is delivered, and one or moreorifices through which gas exits into the mixture. The orifices may bewithin the shroud 208, to enhance mixing, and/or at other locationsalong the length of the shaft 204.

The impeller 210 may have any desired geometry that will draw liquidthrough the shroud at a high velocity. The impeller is preferably amarine impeller, as shown in FIG. 10A, but may have a different design,for example, a Rushton impeller as shown in FIG. 10B, or a modifiedRushton impeller, e.g., tilted so as to provide some axial flow.

In order to generate the high velocity flow through the shroud, themotor 202 is preferably a high speed, high torque motor, e.g., capableof operating at 500 to 20,000 RPM, e.g., 3,000 to 10,000 RPM. However,the larger the mixer (e.g., the larger the shroud and/or the larger themotor) the lower the rotational speed can be. Thus, if a large mixer isused, such as a 5 hp, 10 hp, 20 hp, or 30 hp or greater, the motor maybe designed to operate at lower rotational speeds, e.g., less than 2000RPM, less than 1500 RPM, or even 500 RPM or less. For example, a mixersized to mix a 10,000-20,000 liter tank may operate at speeds of 900 to1,200 RPM. The torque of the motor is preferably self-adjusting, tomaintain a relatively constant impeller speed as the mixing conditionschange over time, e.g., due to saccharification of the solids.

Advantageously, the mixer can be oriented at any desired angle orlocation in the tank, to direct the jet flow in a desired direction.Moreover, as discussed above, depending on the direction of rotation ofthe impeller the mixer can be used to draw fluid from either end of theshroud.

In some implementations, two or more jet mixers are positioned in thevessel, with one or more being configured to jet fluid upward (“uppump”) and one or more being configured to jet fluid downward (“downpump”). In some cases, an up pumping mixer will be positioned adjacent adown pumping mixer, to enhance the turbulent flow created by the mixers.If desired, one or more mixers may be switched between upward flow anddownward flow during processing. It may be advantageous to switch all ormost of the mixers to up pumping mode during initial dispersion of thefeedstock in the liquid medium, particularly if the feedstock is dumpedor blown onto the surface of the liquid, as up pumping createssignificant turbulence at the surface. Up pumping can also be usedduring fermentation to help remove CO2 from the liquid by causing thegas to bubble to the surface where it can be vented.

Other suitable jet mixers are described in U.S. Provisional ApplicationNo. 61/218,832, filed Jun. 19, 2009, and U.S. Ser. No. 12/782,694, filedMay 24, 2010, the full disclosures of which are incorporated herein byreference.

Materials Biomass Materials

The biomass can be, e.g., a cellulosic or lignocellulosic material. Suchmaterials include paper and paper products (e.g., polycoated paper andKraft paper), wood, wood-related materials, e.g., particle board,grasses, rice hulls, bagasse, jute, hemp, flax, bamboo, sisal, abaca,straw, switchgrass, alfalfa, hay, corn cobs, corn stover, coconut hair;and materials high in α-cellulose content, e.g., cotton. Feedstocks canbe obtained from virgin scrap textile materials, e.g., remnants, postconsumer waste, e.g., rags. When paper products are used they can bevirgin materials, e.g., scrap virgin materials, or they can bepost-consumer waste. Aside from virgin raw materials, post-consumer,industrial (e.g., offal), and processing waste (e.g., effluent frompaper processing) can also be used as fiber sources. Biomass feedstockscan also be obtained or derived from human (e.g., sewage), animal orplant wastes. Additional cellulosic and lignocellulosic materials havebeen described in U.S. Pat. Nos. 6,448,307, 6,258,876, 6,207,729,5,973,035 and 5,952,105.

In some embodiments, the biomass material includes a carbohydrate thatis or includes a material having one or more β-1,4-linkages and having anumber average molecular weight between about 3,000 and 50,000. Such acarbohydrate is or includes cellulose (I), which is derived from(β-glucose 1) through condensation of β(1,4)-glycosidic bonds. Thislinkage contrasts itself with that for α(1,4)-glycosidic bonds presentin starch and other carbohydrates.

Starchy materials include starch itself, e.g., corn starch, wheatstarch, potato starch or rice starch, a derivative of starch, or amaterial that includes starch, such as an edible food product or a crop.For example, the starchy material can be arracacha, buckwheat, banana,barley, cassaya, kudzu, oca, sago, sorghum, regular household potatoes,sweet potato, taro, yams, or one or more beans, such as favas, lentilsor peas. Blends of any two or more starchy materials are also starchymaterials.

In some cases the biomass is a microbial material. Microbial sourcesinclude, but are not limited to, any naturally occurring or geneticallymodified microorganism or organism that contains or is capable ofproviding a source of carbohydrates (e.g., cellulose), for example,protists, e.g., animal protists (e.g., protozoa such as flagellates,amoeboids, ciliates, and sporozoa) and plant protists (e.g., algae suchalveolates, chlorarachniophytes, cryptomonads, euglenids, glaucophytes,haptophytes, red algae, stramenopiles, and viridaeplantae). Otherexamples include seaweed, plankton (e.g., macroplankton, mesoplankton,microplankton, nanoplankton, picoplankton, and femtoplankton),phytoplankton, bacteria (e.g., gram positive bacteria, gram negativebacteria, and extremophiles), yeast and/or mixtures of these. In someinstances, microbial biomass can be obtained from natural sources, e.g.,the ocean, lakes, bodies of water, e.g., salt water or fresh water, oron land. Alternatively or in addition, microbial biomass can be obtainedfrom culture systems, e.g., large scale dry and wet culture systems.

Saccharifying Agents

Suitable enzymes include cellobiases and cellulases capable of degradingbiomass.

Suitable cellobiases include a cellobiase from Aspergillus niger soldunder the tradename NOVOZYME 188™.

Cellulases are capable of degrading biomass, and may be of fungal orbacterial origin. Suitable enzymes include cellulases from the generaBacillus, Pseudomonas, Humicola, Fusarium, Thielavia, Acremonium,Chrysosporium and Trichoderma, and include species of Humicola,Coprinus, Thielavia, Fusarium, Myceliophthora, Acremonium,Cephalosporium, Scytalidium, Penicillium or Aspergillus (see, e.g., EP458162), especially those produced by a strain selected from the speciesHumicola insolens (reclassified as Scytalidium thermophilum, see, e.g.,U.S. Pat. No. 4,435,307), Coprinus cinereus, Fusarium oxysporum,Myceliophthora thermophila, Meripilus giganteus, Thielavia terrestris,Acremonium sp., Acremonium persicinum, Acremonium acremonium, Acremoniumbrachypenium, Acremonium dichromosporum, Acremonium obclavatum,Acremonium pinkertoniae, Acremonium roseogriseum, Acremoniumincoloratum, and Acremonium furatum; preferably from the speciesHumicola insolens DSM 1800, Fusarium oxysporum DSM 2672, Myceliophthorathermophila CBS 117.65, Cephalosporium sp. RYM-202, Acremonium sp. CBS478.94, Acremonium sp. CBS 265.95, Acremonium persicinum CBS 169.65,Acremonium acremonium AHU 9519, Cephalosporium sp. CBS 535.71,Acremonium brachypenium CBS 866.73, Acremonium dichromosporum CBS683.73, Acremonium obclavatum CBS 311.74, Acremonium pinkertoniae CBS157.70, Acremonium roseogriseum CBS 134.56, Acremonium incoloratum CBS146.62, and Acremonium furatum CBS 299.70H. Cellulolytic enzymes mayalso be obtained from Chrysosporium, preferably a strain ofChrysosporium lucknowense. Additionally, Trichoderma (particularlyTrichoderma viride, Trichoderma reesei, and Trichoderma koningii),alkalophilic Bacillus (see, for example, U.S. Pat. No. 3,844,890 and EP458162), and Streptomyces (see, e.g., EP 458162) may be used.

Enzyme complexes may be utilized, such as those available from Genencoreunder the tradename ACCELLERASE®, for example, Accellerase® 1500 enzymecomplex. Accellerase® 1500 enzyme complex contains multiple enzymeactivities, mainly exoglucanase, endoglucanase (2200-2800 CMC U/g),hemi-cellulase, and beta-glucosidase (525-775 pNPG U/g), and has a pH of4.6 to 5.0. The endoglucanase activity of the enzyme complex isexpressed in carboxymethylcellulose activity units (CMC U), while thebeta-glucosidase activity is reported in pNP-glucoside activity units(pNPG U). In one embodiment, a blend of Accellerase® 1500 enzyme complexand NOVOZYME™ 188 zcellobiase is used.

In some implementations, the saccharifying agent comprises an acid,e.g., a mineral acid. When an acid is used, co-products may be generatedthat are toxic to microorganisms, in which case the process can furtherinclude removing such co-products. Removal may be performed using anactivated carbon, e.g., activated charcoal, or other suitabletechniques.

Fermentation Agents

The microorganism(s) used in fermentation can be natural microorganismsand/or engineered microorganisms. For example, the microorganism can bea bacterium, e.g., a cellulolytic bacterium, a fungus, e.g., a yeast, aplant or a protist, e.g., an algae, a protozoa or a fungus-like protist,e.g., a slime mold. When the organisms are compatible, mixtures oforganisms can be utilized.

Suitable fermenting microorganisms have the ability to convertcarbohydrates, such as glucose, xylose, arabinose, mannose, galactose,oligosaccharides or polysaccharides into fermentation products.Fermenting microorganisms include strains of the genus Saccharomycesspp. e.g., Saccharomyces cerevisiae (baker's yeast), Saccharomycesdistaticus, Saccharomyces uvarum; the genus Kluyveromyces, e.g., speciesKluyveromyces marxianus, Kluyveromyces fragilis; the genus Candida,e.g., Candida pseudotropicalis, and Candida brassicae, Pichia stipitis(a relative of Candida shehatae, the genus Clavispora, e.g., speciesClavispora lusitaniae and Clavispora opuntiae, the genus Pachysolen,e.g., species Pachysolen tannophilus, the genus Bretannomyces, e.g.,species Bretannomyces clausenii (Philippidis, G. P., 1996, Cellulosebioconversion technology, in Handbook on Bioethanol: Production andUtilization, Wyman, C. E., ed., Taylor & Francis, Washington, D.C.,179-212).

Commercially available yeasts include, for example, Red Star®/LesaffreEthanol Red (available from Red Star/Lesaffre, USA), FALI® (availablefrom Fleischmann's Yeast, a division of Burns Philip Food Inc., USA),SUPERSTART® (available from Alltech, now Lalemand), GERT STRAND®(available from Gert Strand AB, Sweden) and FERMOL® (available from DSMSpecialties).

Bacteria may also be used in fermentation, e.g., Zymomonas mobilis andClostridium thermocellum (Philippidis, 1996, supra).

Additives

Antibiotics

While it is generally preferred to have a high sugar concentration inthe saccharified solution, lower concentrations may be used, in whichcase it may be desirable to add an antimicrobial additive, e.g., a broadspectrum antibiotic, in a low concentration, e.g., 50 to 150 ppm. Othersuitable antibiotics include amphotericin B, ampicillin,chloramphenicol, ciprofloxacin, gentamicin, hygromycin B, kanamycin,neomycin, penicillin, puromycin, streptomycin. Antibiotics will inhibitgrowth of microorganisms during transport and storage, and can be usedat appropriate concentrations, e.g., between 15 and 1000 ppm by weight,e.g., between 25 and 500 ppm, or between 50 and 150 ppm. If desired, anantibiotic can be included even if the sugar concentration is relativelyhigh.

Surfactants

The addition of surfactants can enhance the rate of saccharification.Examples of surfactants include non-ionic surfactants, such as a Tween®20 or Tween® 80 polyethylene glycol surfactants, ionic surfactants, oramphoteric surfactants. Other suitable surfactants include octylphenolethoxylates such as the TRITON™ X series nonionic surfactantscommercially available from Dow Chemical. A surfactant can also be addedto keep the sugar that is being produced in solution, particularly inhigh concentration solutions.

Saccharification Medium

In one embodiment, the medium has the following concentrations ofcomponents:

Yeast nitrogen base  1.7 g/L Urea 2.27 g/L Peptone 6.56 g/L Tween ® 80surfactant  10 g/L

Physical Treatment of Feedstock

Physical Preparation

In some cases, methods can include a physical preparation, e.g., sizereduction of materials, such as by cutting, grinding, shearing,pulverizing or chopping. For example, in some cases, loose feedstock(e.g., recycled paper, starchy materials, coal or switchgrass) isprepared by shearing or shredding. For example, in other cases, materialis first pretreated or processed using one or more any of the methodsdescribed herein, such as radiation, sonication, oxidation, pyrolysis orsteam explosion, and then size reduced or further size reduced. Treatingfirst and then size reducing can be advantageous since treated materialstend to be more brittle and, therefore, easier to size reduce. Screensand/or magnets can be used to remove oversized or undesirable objectssuch as, for example, rocks or nails from the feed stream.

Feed preparation systems can be configured to produce streams withspecific characteristics such as, for example, specific maximum sizes,specific length-to-width, or specific surface areas ratios. Physicalpreparation can increase the rate of reactions or reduce the processingtime required by opening up the materials and making them moreaccessible to processes and/or reagents, such as reagents in a solution.The bulk density of feedstocks can be controlled (e.g., increased). Insome situations, it can be desirable to prepare a low bulk densitymaterial, densify the material (e.g., to make it easier and less costlyto transport to another site), and then revert the material to a lowerbulk density state.

Size Reduction

In some embodiments, the material to be processed is in the form of afibrous material that includes fibers provided by shearing a fibersource. For example, the shearing can be performed with a rotary knifecutter.

For example, a fiber source, e.g., that is recalcitrant or that has hadits recalcitrance level reduced, can be sheared, e.g., in a rotary knifecutter, to provide a first fibrous material. The first fibrous materialis passed through a first screen, e.g., having an average opening sizeof 1.59 mm or less ( 1/16 inch, 0.0625 inch), provide a second fibrousmaterial. If desired, the fiber source can be cut prior to the shearing,e.g., with a shredder. For example, when a paper is used as the fibersource, the paper can be first cut into strips that are, e.g., ¼- to½-inch wide, using a shredder, e.g., a counter-rotating screw shredder,such as those manufactured by Munson (Utica, N.Y.). As an alternative toshredding, the paper can be reduced in size by cutting to a desired sizeusing a guillotine cutter. For example, the guillotine cutter can beused to cut the paper into sheets that are, e.g., 10 inches wide by 12inches long.

In some embodiments, the shearing of the fiber source and the passing ofthe resulting first fibrous material through a first screen areperformed concurrently. The shearing and the passing can also beperformed in a batch-type process.

For example, a rotary knife cutter can be used to concurrently shear thefiber source and screen the first fibrous material. A rotary knifecutter includes a hopper that can be loaded with a shredded fiber sourceprepared by shredding a fiber source. The shredded fiber source. In someimplementations, the feedstock is physically treated prior tosaccharification and/or fermentation. Physical treatment processes caninclude one or more of any of those described herein, such as mechanicaltreatment, chemical treatment, irradiation, sonication, oxidation,pyrolysis or steam explosion. Treatment methods can be used incombinations of two, three, four, or even all of these technologies (inany order). When more than one treatment method is used, the methods canbe applied at the same time or at different times. Other processes thatchange a molecular structure of a biomass feedstock may also be used,alone or in combination with the processes disclosed herein.

Mechanical Treatments

In some cases, methods can include mechanically treating the biomassfeedstock. Mechanical treatments include, for example, cutting, milling,pressing, grinding, shearing and chopping. Milling may include, forexample, ball milling, hammer milling, rotor/stator dry or wet milling,or other types of milling. Other mechanical treatments include, e.g.,stone grinding, cracking, mechanical ripping or tearing, pin grinding orair attrition milling.

Mechanical treatment can be advantageous for “opening up,” “stressing,”breaking and shattering the cellulosic or lignocellulosic materials,making the cellulose of the materials more susceptible to chain scissionand/or reduction of crystallinity. The open materials can also be moresusceptible to oxidation when irradiated.

In some cases, the mechanical treatment may include an initialpreparation of the feedstock as received, e.g., size reduction ofmaterials, such as by cutting, grinding, shearing, pulverizing orchopping. For example, in some cases, loose feedstock (e.g., recycledpaper, starchy materials, or switchgrass) is prepared by shearing orshredding.

Alternatively, or in addition, the feedstock material can first bephysically treated by one or more of the other physical treatmentmethods, e.g., chemical treatment, radiation, sonication, oxidation,pyrolysis or steam explosion, and then mechanically treated. Thissequence can be advantageous since materials treated by one or more ofthe other treatments, e.g., irradiation or pyrolysis, tend to be morebrittle and, therefore, it may be easier to further change the molecularstructure of the material by mechanical treatment.

In some embodiments, the feedstock material is in the form of a fibrousmaterial, and mechanical treatment includes shearing to expose fibers ofthe fibrous material. Shearing can be performed, for example, using arotary knife cutter. Other methods of mechanically treating thefeedstock include, for example, milling or grinding. Milling may beperformed using, for example, a hammer mill, ball mill, colloid mill,conical or cone mill, disk mill, edge mill, Wiley mill or grist mill.Grinding may be performed using, for example, a stone grinder, pingrinder, coffee grinder, or burr grinder. Grinding may be provided, forexample, by a reciprocating pin or other element, as is the case in apin mill. Other mechanical treatment methods include mechanical rippingor tearing, other methods that apply pressure to the material, and airattrition milling. Suitable mechanical treatments further include anyother technique that changes the molecular structure of the feedstock.

If desired, the mechanically treated material can be passed through ascreen, e.g., having an average opening size of 1.59 mm or less ( 1/16inch, 0.0625 inch). In some embodiments, shearing, or other mechanicaltreatment, and screening are performed concurrently. For example, arotary knife cutter can be used to concurrently shear and screen thefeedstock. The feedstock is sheared between stationary blades androtating blades to provide a sheared material that passes through ascreen, and is captured in a bin.

The cellulosic or lignocellulosic material can be mechanically treatedin a dry state (e.g., having little or no free water on its surface), ahydrated state (e.g., having up to ten percent by weight absorbedwater), or in a wet state, e.g., having between about 10 percent andabout 75 percent by weight water. The fiber source can even bemechanically treated while partially or fully submerged under a liquid,such as water, ethanol or isopropanol.

The cellulosic or lignocellulosic material can also be mechanicallytreated under a gas (such as a stream or atmosphere of gas other thanair), e.g., oxygen or nitrogen, or steam.

If desired, lignin can be removed from any of the fibrous materials thatinclude lignin. Also, to aid in the breakdown of the materials thatinclude cellulose, the material can be treated prior to or duringmechanical treatment or irradiation with heat, a chemical (e.g., mineralacid, base or a strong oxidizer such as sodium hypochlorite) and/or anenzyme. For example, grinding can be performed in the presence of anacid.

Mechanical treatment systems can be configured to produce streams withspecific morphology characteristics such as, for example, surface area,porosity, bulk density, and, in the case of fibrous feedstocks, fibercharacteristics such as length-to-width ratio.

In some embodiments, a BET surface area of the mechanically treatedmaterial is greater than 0.1 m2/g, e.g., greater than 0.25 m2/g, greaterthan 0.5 m2/g, greater than 1.0 m2/g, greater than 1.5 m2/g, greaterthan 1.75 m2/g, greater than 5.0 m2/g, greater than 10 m2/g, greaterthan 25 m2/g, greater than 35 m2/g, greater than 50 m2/g, greater than60 m2/g, greater than 75 m2/g, greater than 100 m2/g, greater than 150m2/g, greater than 200 m2/g, or even greater than 250 m2/g.

A porosity of the mechanically treated material can be, e.g., greaterthan 20 percent, greater than 25 percent, greater than 35 percent,greater than 50 percent, greater than 60 percent, greater than 70percent, greater than 80 percent, greater than 85 percent, greater than90 percent, greater than 92 percent, greater than 94 percent, greaterthan 95 percent, greater than 97.5 percent, greater than 99 percent, oreven greater than 99.5 percent.

In some embodiments, after mechanical treatment the material has a bulkdensity of less than 0.25 g/cm3, e.g., 0.20 g/cm3, 0.15 g/cm3, 0.10g/cm3, 0.05 g/cm3 or less, e.g., 0.025 g/cm3. Bulk density is determinedusing ASTM D1895B. Briefly, the method involves filling a measuringcylinder of known volume with a sample and obtaining a weight of thesample. The bulk density is calculated by dividing the weight of thesample in grams by the known volume of the cylinder in cubiccentimeters.

If the feedstock is a fibrous material the fibers of the fibrousmaterials mechanically treated material can have a relatively largeaverage length-to-diameter ratio (e.g., greater than 20-to-1), even ifthey have been sheared more than once. In addition, the fibers of thefibrous materials described herein may have a relatively narrow lengthand/or length-to-diameter ratio distribution.

As used herein, average fiber widths (e.g., diameters) are thosedetermined optically by randomly selecting approximately 5,000 fibers.Average fiber lengths are corrected length-weighted lengths. BET(Brunauer, Emmet and Teller) surface areas are multi-point surfaceareas, and porosities are those determined by mercury porosimetry.

If the second feedstock is a fibrous material 14 the averagelength-to-diameter ratio of fibers of the mechanically treated materialcan be, e.g. greater than 8/1, e.g., greater than 10/1, greater than15/1, greater than 20/1, greater than 25/1, or greater than 50/1. Anaverage fiber length of the mechanically treated material 14 can be,e.g., between about 0.5 mm and 2.5 mm, e.g., between about 0.75 mm and1.0 mm, and an average width (e.g., diameter) of the second fibrousmaterial 14 can be, e.g., between about 5 μm and 50 μm, e.g., betweenabout 10 μm and 30 μm.

In some embodiments, if the feedstock is a fibrous material, thestandard deviation of the fiber length of the mechanically treatedmaterial can be less than 60 percent of an average fiber length of themechanically treated material, e.g., less than 50 percent of the averagelength, less than 40 percent of the average length, less than 25 percentof the average length, less than 10 percent of the average length, lessthan 5 percent of the average length, or even less than 1 percent of theaverage length.

In some situations, it can be desirable to prepare a low bulk densitymaterial, densify the material (e.g., to make it easier and less costlyto transport to another site), and then revert the material to a lowerbulk density state. Densified materials can be processed by any of themethods described herein, or any material processed by any of themethods described herein can be subsequently densified, e.g., asdisclosed in U.S. Ser. No. 12/429,045 and WO 2008/073186, the fulldisclosures of which are incorporated herein by reference.

Treatment to Solubilize, Reduce Recalcitrance or Functionalize

Materials that have or have not been physically prepared can be treatedfor use in any production process described herein. One or more of theproduction processes described below may be included in therecalcitrance reducing operating unit discussed above. Alternatively, orin addition, other processes for reducing recalcitrance may be included.

Treatment processes utilized by the recalcitrance reducing operatingunit can include one or more of irradiation, sonication, oxidation,pyrolysis or steam explosion. Treatment methods can be used incombinations of two, three, four, or even all of these technologies (inany order).

Radiation Treatment

One or more radiation processing sequences can be used to processmaterials from the feedstock, and to provide a wide variety of differentsources to extract useful substances from the feedstock, and to providepartially degraded structurally modified material which functions asinput to further processing steps and/or sequences. Irradiation can, forexample, reduce the molecular weight and/or crystallinity of feedstock.Radiation can also sterilize the materials, or any media needed tobioprocess the material.

In some embodiments, energy deposited in a material that releases anelectron from its atomic orbital is used to irradiate the materials. Theradiation may be provided by (1) heavy charged particles, such as alphaparticles or protons, (2) electrons, produced, for example, in betadecay or electron beam accelerators, or (3) electromagnetic radiation,for example, gamma rays, x rays, or ultraviolet rays. In one approach,radiation produced by radioactive substances can be used to irradiatethe feedstock. In some embodiments, any combination in any order orconcurrently of (1) through (3) may be utilized. In another approach,electromagnetic radiation (e.g., produced using electron beam emitters)can be used to irradiate the feedstock. The doses applied depend on thedesired effect and the particular feedstock.

In some instances when chain scission is desirable and/or polymer chainfunctionalization is desirable, particles heavier than electrons, suchas protons, helium nuclei, argon ions, silicon ions, neon ions, carbonions, phosphorus ions, oxygen ions or nitrogen ions can be utilized.When ring-opening chain scission is desired, positively chargedparticles can be utilized for their Lewis acid properties for enhancedring-opening chain scission. For example, when maximum oxidation isdesired, oxygen ions can be utilized, and when maximum nitration isdesired, nitrogen ions can be utilized. The use of heavy particles andpositively charged particles is described in U.S. Ser. No. 12/417,699,the full disclosure of which is incorporated herein by reference.

In one method, a first material that is or includes cellulose having afirst number average molecular weight (MN1) is irradiated, e.g., bytreatment with ionizing radiation (e.g., in the form of gamma radiation,X-ray radiation, 100 nm to 280 nm ultraviolet (UV) light, a beam ofelectrons or other charged particles) to provide a second material thatincludes cellulose having a second number average molecular weight (MN2)lower than the first number average molecular weight. The secondmaterial (or the first and second material) can be combined with amicroorganism (with or without enzyme treatment) that can utilize thesecond and/or first material or its constituent sugars or lignin toproduce an intermediate or a product, such as those described herein.

Since the second material includes cellulose having a reduced molecularweight relative to the first material, and in some instances, a reducedcrystallinity as well, the second material is generally moredispersible, swellable and/or soluble, e.g., in a solution containing amicroorganism and/or an enzyme. These properties make the secondmaterial easier to process and more susceptible to chemical, enzymaticand/or biological attack relative to the first material, which cangreatly improve the production rate and/or production level of a desiredproduct, e.g., ethanol. Radiation can also sterilize the materials orany media needed to bioprocess the material.

In some embodiments, the second material can have a level of oxidation(O2) that is higher than the level of oxidation (O1) of the firstmaterial. A higher level of oxidation of the material can aid in itsdispersability, swellability and/or solubility, further enhancing thematerial's susceptibility to chemical, enzymatic or biological attack.In some embodiments, to increase the level of the oxidation of thesecond material relative to the first material, the irradiation isperformed under an oxidizing environment, e.g., under a blanket of airor oxygen, producing a second material that is more oxidized than thefirst material. For example, the second material can have more hydroxylgroups, aldehyde groups, ketone groups, ester groups or carboxylic acidgroups, which can increase its hydrophilicity.

Ionizing Radiation

Each form of radiation ionizes the carbon-containing material viaparticular interactions, as determined by the energy of the radiation.Heavy charged particles primarily ionize matter via Coulomb scattering;furthermore, these interactions produce energetic electrons that mayfurther ionize matter. Alpha particles are identical to the nucleus of ahelium atom and are produced by the alpha decay of various radioactivenuclei, such as isotopes of bismuth, polonium, astatine, radon,francium, radium, several actinides, such as actinium, thorium, uranium,neptunium, curium, californium, americium, and plutonium.

When particles are utilized, they can be neutral (uncharged), positivelycharged or negatively charged. When charged, the charged particles canbear a single positive or negative charge, or multiple charges, e.g.,one, two, three or even four or more charges. In instances in whichchain scission is desired, positively charged particles may bedesirable, in part due to their acidic nature. When particles areutilized, the particles can have the mass of a resting electron, orgreater, e.g., 500, 1000, 1500, 2000, 10,000 or even 100,000 times themass of a resting electron. For example, the particles can have a massof from about 1 atomic unit to about 150 atomic units, e.g., from about1 atomic unit to about 50 atomic units, or from about 1 to about 25,e.g., 1, 2, 3, 4, 5, 10, 12 or 15 amu. Accelerators used to acceleratethe particles can be electrostatic DC, electrodynamic DC, RF linear,magnetic induction linear or continuous wave. For example, cyclotrontype accelerators are available from IBA, Belgium, such as theRhodotron® system, while DC type accelerators are available from RDI,now IBA Industrial, such as the Dynamitron®. Ions and ion acceleratorsare discussed in Introductory Nuclear Physics, Kenneth S. Krane, JohnWiley & Sons, Inc. (1988), Krsto Prelec, FIZIKA B 6 (1997) 4, 177-206,Chu, William T., “Overview of Light-Ion Beam Therapy” Columbus-Ohio,ICRU-IAEA Meeting, 18-20 Mar. 2006, Iwata, Y. et al.,“Alternating-Phase-Focused IH-DTL for Heavy-Ion Medical Accelerators”Proceedings of EPAC 2006, Edinburgh, Scotland and Leaner, C. M. et al.,“Status of the Superconducting ECR Ion Source Venus” Proceedings of EPAC2000, Vienna, Austria.

In some embodiments, a beam of electrons is used as the radiationsource. A beam of electrons has the advantages of high dose rates (e.g.,1, 5, or even 10 Mrad per second), high throughput, less containment,and less confinement equipment. Electrons can also be more efficient atcausing chain scission. In addition, electrons having energies of 4-10MeV can have a penetration depth of 5 to 30 mm or more, such as 40 mm.In some cases, multiple electron beam devices (e.g., multiple heads,often referred to as “horns”) are used to deliver multiple doses ofelectron beam radiation to the material. This high total beam power isusually achieved by utilizing multiple accelerating heads. For example,the electron beam device may include two, four, or more acceleratingheads. As one example, the electron beam device may include fouraccelerating heads, each of which has a beam power of 300 kW, for atotal beam power of 1200 kW. The use of multiple heads, each of whichhas a relatively low beam power, prevents excessive temperature rise inthe material, thereby preventing burning of the material, and alsoincreases the uniformity of the dose through the thickness of the layerof material. Irradiating with multiple heads is disclosed in U.S.Provisional Application No. 61/394,851, filed Oct. 20, 2010, thecomplete disclosure of which is incorporated herein by reference.

Electron beams can be generated, e.g., by electrostatic generators,cascade generators, transformer generators, low energy accelerators witha scanning system, low energy accelerators with a linear cathode, linearaccelerators, and pulsed accelerators. Electrons as an ionizingradiation source can be useful, e.g., for relatively thin piles ofmaterials, e.g., less than 0.5 inch, e.g., less than 0.4 inch, 0.3 inch,0.2 inch, or less than 0.1 inch. In some embodiments, the energy of eachelectron of the electron beam is from about 0.3 MeV to about 2.0 MeV(million electron volts), e.g., from about 0.5 MeV to about 1.5 MeV, orfrom about 0.7 MeV to about 1.25 MeV.

Electron beam irradiation devices may be procured commercially from IonBeam Applications, Louvain-la-Neuve, Belgium or the Titan Corporation,San Diego, Calif. Typical electron energies can be 1 MeV, 2 MeV, 4.5MeV, 7.5 MeV, or 10 MeV. Typical electron beam irradiation device powercan be 1 kW, 5 kW, 10 kW, 20 kW, 50 kW, 100 kW, 250 kW, or 500 kW. Thelevel of depolymerization of the feedstock depends on the electronenergy used and the dose applied, while exposure time depends on thepower and dose. Typical doses may take values of 1 kGy, 5 kGy, 10 kGy,20 kGy, 50 kGy, 100 kGy, or 200 kGy.

Electromagnetic Radiation

In embodiments in which the irradiating is performed withelectromagnetic radiation, the electromagnetic radiation can have, e.g.,energy per photon (in electron volts) of greater than 102 eV, e.g.,greater than 103, 104, 105, 106, or even greater than 107 eV. In someembodiments, the electromagnetic radiation has energy per photon ofbetween 104 and 107, e.g., between 105 and 106 eV. The electromagneticradiation can have a frequency of, e.g., greater than 1016 Hz, greaterthan 1017 Hz, 1018, 1019, 1020, or even greater than 1021 Hz. In someembodiments, the electromagnetic radiation has a frequency of between1018 and 1022 Hz, e.g., between 1019 to 1021 Hz.

Doses

In some embodiments, the irradiating (with any radiation source or acombination of sources) is performed until the material receives a doseof at least 0.25 Mrad, e.g., at least 1.0, 2.5, 5.0, 8.0, 10, 15, 20,25, 30, 35, 40, 50, or even at least 100 Mrad. In some embodiments, theirradiating is performed until the material receives a dose of between1.0 Mrad and 6.0 Mrad, e.g., between 1.5 Mrad and 4.0 Mrad, 2 Mrad and10 Mrad, 5 Mrad and 20 Mrad, 10 Mrad and 30 Mrad, 10 Mrad and 40 Mrad,or 20 Mrad and 50 Mrad.

In some embodiments, the irradiating is performed at a dose rate ofbetween 5.0 and 1500.0 kilorads/hour, e.g., between 10.0 and 750.0kilorads/hour or between 50.0 and 350.0 kilorads/hours.

In some embodiments, two or more radiation sources are used, such as twoor more ionizing radiations. For example, samples can be treated, in anyorder, with a beam of electrons, followed by gamma radiation and UVlight having wavelengths from about 100 nm to about 280 nm. In someembodiments, samples are treated with three ionizing radiation sources,such as a beam of electrons, gamma radiation, and energetic UV light.

Sonication, Pyrolysis and Oxidation

In addition to radiation treatment, the feedstock may be treated withany one or more of sonication, pyrolysis and oxidation. These treatmentprocesses are described in U.S. Ser. No. 12/417,840, the disclosure ofwhich is incorporated by reference herein.

Other Processes to Solubilize, Reduce Recalcitrance or to Functionalize

Any of the processes of this paragraph can be used alone without any ofthe processes described herein, or in combination with any of theprocesses described herein (in any order): steam explosion, chemicaltreatment (e.g., acid treatment (including concentrated and dilute acidtreatment with mineral acids, such as sulfuric acid, hydrochloric acidand organic acids, such as trifluoroacetic acid), and/or base treatment(e.g., treatment with lime or sodium hydroxide)), UV treatment, screwextrusion treatment (see, e.g., U.S. Patent Application Ser. No.61/115,398, filed Nov. 17, 2008), solvent treatment (e.g., treatmentwith ionic liquids) and freeze milling (see, e.g., U.S. PatentApplication Ser. No. 61/081,709 and Ser. No. 12/502,629).

Production of Fuels, Acids, Esters, and/or Other Products

After one or more of the processing steps discussed above have beenperformed on the biomass, the complex carbohydrates contained in thecellulose and hemicellulose fractions can be processed into fermentablesugars using a saccharification process, as discussed above.

After the resulting sugar solution has been transported to amanufacturing facility, the sugars can be converted into a variety ofproducts, such as alcohols, e.g., ethanol, or organic acids. The productobtained depends upon the microorganism utilized and the conditionsunder which the bioprocessing occurs. These steps can be performed, forexample, utilizing the existing equipment of the corn-based ethanolmanufacturing facility.

The mixing processes and equipment discussed herein may also be usedduring bioprocessing, if desired. Advantageously, the mixing systemsdescribed herein do not impart high shear to the liquid, and do notsignificantly raise the overall temperature of the liquid. As a result,the microorganisms used in bioprocessing are maintained in a viablecondition throughout the process. Mixing may enhance the reaction rateand improve the efficiency of the process.

Generally, fermentation utilizes various microorganisms. The sugarsolution produced by saccharification of lignocellulosic materials willgenerally contain xylose as well as glucose. It may be desirable toremove the xylose, e.g., by chromatography, as some commonly usedmicroorganisms (e.g., yeasts) do not act on xylose. The xylose may becollected and utilized in the manufacture of other products, e.g.,animal feeds and the sweetener Xylitol. The xylose may be removed priorto or after delivery of the sugar solution to the manufacturing facilitywhere fermentation will be performed.

The microorganism can be a natural microorganism or an engineeredmicroorganism, e.g., any of the microorganisms discussed in theMaterials section herein.

The optimum pH for yeast is from about pH 4 to 5, while the optimum pHfor Zymomonas is from about pH 5 to 6. Typical fermentation times areabout 24 to 96 hours with temperatures in the range of 26° C. to 40° C.,however thermophilic microorganisms prefer higher temperatures.

Carboxylic acid groups generally lower the pH of the fermentationsolution, tending to inhibit fermentation with some microorganisms, suchPichia stipitis. Accordingly, it is in some cases desirable to add baseand/or a buffer, before or during fermentation, to bring up the pH ofthe solution. For example, sodium hydroxide or lime can be added to thefermentation medium to elevate the pH of the medium to range that isoptimum for the microorganism utilized.

Fermentation is generally conducted in an aqueous growth medium, whichcan contain a nitrogen source or other nutrient source, e.g., urea,along with vitamins and trace minerals and metals. It is generallypreferable that the growth medium be sterile, or at least have a lowmicrobial load, e.g., bacterial count. Sterilization of the growthmedium may be accomplished in any desired manner. However, in preferredimplementations, sterilization is accomplished by irradiating the growthmedium or the individual components of the growth medium prior tomixing. The dosage of radiation is generally as low as possible whilestill obtaining adequate results, in order to minimize energyconsumption and resulting cost. For example, in many instances, thegrowth medium itself or components of the growth medium can be treatedwith a radiation dose of less than 5 Mrad, such as less than 4, 3, 2 or1 Mrad. In specific instances, the growth medium is treated with a doseof between about 1 and 3 Mrad.

In some embodiments, all or a portion of the fermentation process can beinterrupted before the low molecular weight sugar is completelyconverted to ethanol. The intermediate fermentation products includehigh concentrations of sugar and carbohydrates. These intermediatefermentation products can be used in preparation of food for human oranimal consumption. Additionally or alternatively, the intermediatefermentation products can be ground to a fine particle size in astainless-steel laboratory mill to produce a flour-like substance.

Mobile fermenters can be utilized, as described in U.S. ProvisionalPatent Application Ser. 60/832,735, now Published InternationalApplication No. WO 2008/011598. Similarly, the saccharificationequipment can be mobile. Further, saccharification and/or fermentationmay be performed in part or entirely during transit.

Post-Processing

After fermentation, the resulting fluids can be distilled using, forexample, a “beer column” to separate ethanol and other alcohols from themajority of water and residual solids. The vapor exiting the beer columncan be, e.g., 35% by weight ethanol and can be fed to a rectificationcolumn. A mixture of nearly azeotropic (92.5%) ethanol and water fromthe rectification column can be purified to pure (99.5%) ethanol usingvapor-phase molecular sieves. The beer column bottoms can be sent to thefirst effect of a three-effect evaporator. The rectification columnreflux condenser can provide heat for this first effect. After the firsteffect, solids can be separated using a centrifuge and dried in a rotarydryer. A portion (25%) of the centrifuge effluent can be recycled tofermentation and the rest sent to the second and third evaporatoreffects. Most of the evaporator condensate can be returned to theprocess as fairly clean condensate with a small portion split off towaste water treatment to prevent build-up of low-boiling compounds.

Intermediates and Products

Using the processes described herein, the treated biomass can beconverted to one or more products, such as energy, fuels, foods andmaterials. Specific examples of products include, but are not limitedto, hydrogen, alcohols (e.g., monohydric alcohols or dihydric alcohols,such as ethanol, n-propanol or n-butanol), hydrated or hydrous alcohols,e.g., containing greater than 10%, 20%, 30% or even greater than 40%water, xylitol, sugars, biodiesel, organic acids (e.g., acetic acidand/or lactic acid), hydrocarbons, co-products (e.g., proteins, such ascellulolytic proteins (enzymes) or single cell proteins), and mixturesof any of these in any combination or relative concentration, andoptionally in combination with any additives, e.g., fuel additives.Other examples include carboxylic acids, such as acetic acid or butyricacid, salts of a carboxylic acid, a mixture of carboxylic acids andsalts of carboxylic acids and esters of carboxylic acids (e.g., methyl,ethyl and n-propyl esters), ketones (e.g., acetone), aldehydes (e.g.,acetaldehyde), alpha, beta unsaturated acids, such as acrylic acid andolefins, such as ethylene. Other alcohols and alcohol derivativesinclude propanol, propylene glycol, 1,4-butanediol, 1,3-propanediol,methyl or ethyl esters of any of these alcohols. Other products includemethyl acrylate, methylmethacrylate, lactic acid, propionic acid,butyric acid, succinic acid, 3-hydroxypropionic acid, a salt of any ofthe acids and a mixture of any of the acids and respective salts.

Other intermediates and products, including food and pharmaceuticalproducts, are described in U.S. Ser. No. 12/417,900, the full disclosureof which is hereby incorporated by reference herein.

Other Embodiments

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure.

In some implementations, the systems discussed herein, or components ofthese systems, may be portable, e.g., in the manner of the mobileprocessing equipment described in U.S. Ser. No. 12/374,549 andInternational Application No. WO 2008/011598, the full disclosures ofwhich are incorporated herein by reference.

In any of the dispersing systems described herein, the flow of fluid(liquid and/or gas) through the dispersing system can be continuous orpulsed, or a combination of periods of continuous flow with intervals ofpulsed flow. When the flow is pulsed, pulsing can be regular orirregular.

While tanks have been referred to herein, the process may take place inany type of vessel or container, including lagoons, pools, ponds and thelike. If the container in which mixing takes place is an in-groundstructure such as a lagoon, it may be lined. The container may becovered, e.g., if it is outdoors, or uncovered.

In an alternate embodiment, the dispersing system 134 can be omitted inthe systems shown in FIGS. 2A and 2B, and a pump can be used to drawliquid from the tank and deliver it through outlet pipe 137 to wet thefeedstock material, which is then dispersed by the mixing action of thejet mixer 144. In such implementations, the pump would preferably be alow shear pump, e.g., a positive displacement pump such as theprogressive cavity pumps available from SEEPEX and lobe pumps fromWaukesha. It is also preferred that the pump be capable of pumping highviscosity fluids, since the viscosity of the liquid will increase asmore feedstock is added.

While biomass feedstocks have been described herein, other feedstocksand mixtures of biomass feedstocks with other feedstocks may be used.For example, some implementations may utilize mixtures of biomassfeedstocks with hydrocarbon-containing feedstocks such as thosedisclosed in U.S. Provisional Application No. 61/226,877, filed Jul. 20,2009, the full disclosure of which is incorporated by reference herein.

Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A feedstock saccharification system comprising: atank configured to contain a biomass feedstock and a liquid medium; adispersing system configured to disperse the biomass feedstock in theliquid medium, and optionally configured to add additional feedstock tothe tank; and a jet mixer configured to mix the contents of the tank;wherein the initial solids concentration of the biomass feedstockdispersed in the liquid medium is at least 20% by weight.
 2. The systemof claim 1, wherein the dispersing system is configured to draw thefeedstock and liquid medium out of the tank and recirculate it back intothe tank.
 3. The system of claim 1, wherein the dispersing systemcomprises a chamber and, within the chamber, a rotating member whichdraws the feedstock and liquid medium into the chamber axially andexpels a dispersion of the feedstock in the medium from the chamberradially.
 4. The system of claim 3, wherein the rotating memberfunctions as an impeller and the action of the rotating member withinthe chamber is that of a centrifugal pump.
 5. The system of claim 3,wherein the rotating member comprises mixing elements arranged coaxiallywith a rotor that is disposed in rotor-stator relationship with a sidewall of the chamber.
 6. The system of claim 1, wherein the dispersingsystem comprises a positive displacement pump.
 7. The system of claim 6,wherein the positive displacement pump comprises a progressive cavitypump.
 8. The system of claim 1, wherein the dispersing system comprisesa plurality of dispersing devices.
 9. The system of claim 1, wherein thedispersing system is configured to deliver a stream of liquid onto thefeedstock on the surface of the liquid, wetting the feedstock.
 10. Thesystem of claim 1, further comprising a delivery system configured todeliver a feedstock from a source disposed outside the tank.
 11. Thesystem of claim 10, wherein the source of the feedstock is positionedabove the tank.
 12. The system of claim 1, further comprising asaccharifying agent delivery device configured to deliver asaccharifying agent from a source disposed outside the tank.
 13. Thesystem of claim 12, wherein the source of the saccharifying agent ispositioned above the tank.
 14. The system of claim 10, wherein thesource of the feedstock comprises a hopper.
 15. The system of claim 14,wherein the hopper comprises a vibrating device.
 16. The system of claim12, wherein the source of the saccharifying agent comprises a hopper.17. The system of claim 16, wherein the hopper comprises a vibratingdevice.
 18. The system of claim 1, wherein the feedstocksaccharification system further comprises a monitoring system.
 19. Thesystem of claim 18, wherein the monitoring system comprises a glucosemonitoring system.
 20. The system of claim 19, wherein the glucosemonitoring system is configured to monitor the glucose level of themixture of feedstock, liquid medium, and saccharifying agent duringsaccharification.
 21. The system of claim 18, wherein the monitoringsystem comprises a viscometer.
 22. The system of claim 18, wherein themonitoring system is configured to monitor the temperature within thetank.
 23. The system of claim 18, wherein the monitoring system isconfigured to measure the oxygen within the tank.
 24. The system ofclaim 18, wherein the monitoring system is configured to measure theethanol within the tank.
 25. The system of claim 1, further comprising acontroller that adjusts the operation of the feedstock delivery deviceand/or the saccharifying agent delivery device based on input from atorque monitor.
 26. The system of claim 10, wherein the delivery systemis configured to add additional feedstock to the tank duringsaccharification.
 27. The system of claim 1, wherein the dispersingsystem is configured to disperse the additional feedstock into theliquid medium.
 28. The system of claim 12, wherein the saccharifyingagent delivery device is configured to add additional saccharifyingagent to the tank during saccharification.
 29. The system of claim 28,wherein the dispersing system is configured to disperse the additionalsaccharifying agent into the liquid medium.
 30. The system of claim 10,wherein the delivery system is configured to deliver a feedstockcomprising cellulosic or lignocellulosic material.
 31. The system ofclaim 10, wherein the delivery system is configured to deliver afeedstock having a bulk density of less than about 0.75 g/cm³.
 32. Thesystem of claim 10, wherein the delivery system is configured to delivera liquid medium comprising water.
 33. The system of claim 12, whereinthe saccharifying agent delivery device is configured to deliver asaccharifying agent comprising an enzyme.
 34. The system of claim 10,wherein the delivery system is configured to add feedstock to the liquidmedium in discrete increments, and the dispersing system is configuredto disperse the feedstock in to the liquid medium before the addition ofanother increment of feedstock.
 35. The system of claim 1, furthercomprising an additive delivery system configured to add additives tothe mixture of feedstock, liquid medium and saccharifying agent.
 36. Thesystem of claim 35, wherein the additive delivery system is configuredto add an emulsifier or surfactant or both to the mixture of feedstock,liquid medium and saccharifying agent.